1. Field of the Invention
The present invention relates generally to a technique for testing electrical properties of particulate material and, more specifically, to an apparatus and method for determining both breakdown voltage and conductivity of developer material.
2. Description of the Prior Art
In electrophotographic applications such as xerography, a charge retentive surface is electrostatically charged, and exposed to a light pattern of an original image to be reproduced for selectively discharging the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate or support member (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is well known, and useful for light lens copying from an original, and/or printing applications from electronically generated or stored originals.
Developer material commonly used in systems for developing latent images on the charge retentive surface typically comprises a mixture of toner and a "carrier" of larger granular beads of a ferrous material. If the developing system is a magnetic brush assembly, magnetizable carrier beads also provide mechanical control for the formation of magnetic brush bristles so that toner can readily be brought into contact with the charge retentive surface. Toner is attracted to the latent image from the carrier beads to form the toner image.
Developer material composition is characterized by electrical properties or parameters, such as breakdown voltage and conductivity. It has been found that the magnitudes of breakdown voltage and conductivity for a given batch of developer material can be used as "signatures" of developer material composition since the magnitudes of the breakdown voltage and the conductivity vary as a function of the composition and processing of the developer material. In some instances, the composition and manufacturing process of the developer material may be varied from batch to batch to accommodate for operational differences among printing apparatuses. For example, one printing apparatus may be designed to use a developer material having a composition that significantly differs from the composition of a developer material used in another printing apparatus. In other instances the composition of developer material may vary among batches simply as a result of error associated with manufacturing the developer material.
To monitor these compositional variations in developer material, it would be desirable to provide an arrangement that measures the breakdown voltage and conductivity both automatically and precisely. The disclosures of the following references, all of which generally relate to automatic testing arrangements, may be pertinent to various aspects of the apparatus and method of the present invention:
U.S. Pat. No. 4,399,502 Patentee: MacDonald et al. Issued: Aug. 16, 1983 PA0 U.S. Pat. No. 4,402,055 Patentee: Lloyd et al. Issued: Aug. 30, 1983 PA0 Petersen et al. "System Controller--A Universal Control Unit for System-Compatible Measuring Instruments" Systems and Equipment pp. 25-29
U.S.Pat. No. 4,399,502 discloses a system for remotely controlling one or more instruments from a control terminal. Each instrument includes a stored menu of operations it can perform under control of the terminal. The terminal further includes means for directing the instrument to perform operations indicated by the menu. The system has a command menu which includes input parameters to control the operation of an instrument, output parameters that an instrument can measure or compute, and procedures that an instrument can perform.
U.S. Pat. No. 4,402,055 discloses an automatic test system controlled by a general purpose digital central processor. The central processor accepts test programs in a high level compiler language. Each program is compacted into a simplified language, the language being used to communicate with test devices through a standard IEEE 488 data bus. Each test device includes a programmable interface digital processor, which interface performs any translation necessary to permit specific test instruments, coupled to the central processor through the interface processor, to perform the tests specified by the high level test program.
The article, entitled "System Controller--A Universal Control Unit for System-Compatible Measuring Instruments," discloses an automatic testing system including a table-top computer for control of instruments compatible with an IEC bus. The controller is capable of solving general mathematical problems as well as evaluating and interpreting the results of measurements and calculations. The system is programmable using BASIC.